An optical network-on-chip system is a technology in which multiple modules with different functions are integrated on a same chip. As a new technology for all-optical switching and short-range interconnection, the optical network-on-chip system has advantages of high reliability, low power consumption, low costs, and the like. FIG. 1 schematically shows an architecture of a switching node 100 in a typical optical network-on-chip system. The switching node 100 includes a substrate 160. A wavelength division demultiplexer 110, an N×M optical switch 120, a wavelength division multiplexer (WDM) 130, a photodetector 140, and a very large scale integrated circuit (VLSI) 150 are disposed on the substrate 160. The VLSI 150 is configured to control at least one electrically-driven component included in the switching node, for example, the photodetector 140. The wavelength division demultiplexer 110 is configured to receive an optical signal that is input from an input fiber and that includes multiple wavelengths, demultiplex the received optical signal into multiple optical signals that each have a single wavelength, and transmit the multiple optical signals to the N×M optical switch 120. The wavelengths of the multiple optical signals are mutually different. The N×M optical switch 120 is configured to receive the multiple optical signals transmitted by the wavelength division demultiplexer 110, determine an output port of each of the multiple optical signals according to destination nodes of the multiple optical signals, and output the multiple optical signals from output ports respectively corresponding to the multiple optical signals. Specifically, for one optical signal of the multiple optical signals, if a destination node of the optical signal is the switching node 100, the N×M optical switch 120 outputs the optical signal by using an output port corresponding to the photodetector 140; if the destination node of the optical signal is another node than the switching node 100, the N×M optical switch 120 outputs the optical signal by using an output port corresponding to the another node. The WDM 130 is configured to receive at least one optical signal transmitted by the N×M optical switch 120, and multiplex the received at least one optical signal into an optical signal including at least one wavelength. The photodetector 140 is configured to receive the at least one optical signal transmitted by the N×M optical switch 120, and convert the received at least one optical signal into an electrical signal.
A mode division multiplexing (MDM) technology can effectively improve performance of an optical network system. Therefore, how to apply the MDM technology to the optical network-on-chip system is a research hotspot in the field. In the MDM technology, a planar multi-mode waveguide is used in a photonic integrated circuit (PIC) to replace a conventional planar single-mode waveguide, and different pieces of information are loaded to orthogonal eigenmodes (eigenmode) of the planar multi-mode waveguide for transmission, where the eigemodes have a same frequency, different spatial energy distribution, and different mode orders. A core of the on-chip MDM technology lies in a mode multiplexer/demultiplexer corresponding to the planar multi-mode waveguide. However, currently, there is no satisfying mode multiplexer/demultiplexer applicable to the optical network-on-chip system.